Method

2. Put 200 g (7 oz/1⅓ cups) of the chocolate in a heatproof bowl with the butter. Set the bowl over a saucepan of simmering water, ensuring the base of the bowl doesn’t touch the water. Stir until the chocolate and butter have melted. Allow to cool.

3. Whisk the eggs and sugar in a large bowl for 5 minutes, or until pale and thick. Fold the cooled chocolate mixture through, then the cocoa powder and flour. Fold in the cashews and remaining chocolate.

4. Pour into the prepared tin, smoothing the surface. Bake for 30–35 minutes, or until just firm to the touch (the mixture will firm on cooling). Remove from the oven and allow to cool.

5. To make the chocolate icing (frosting), put the chocolate in a small heatproof bowl. Set the bowl over a small saucepan of simmering water, ensuring the base of the bowl doesn’t touch the water. Stir until the chocolate has melted. Cool slightly, then mix in the sour cream and icing sugar. Spread over the cooled brownies.

6. Leave for a few hours or overnight to firm up, then cut into squares. Store in an airtight container for up to 5 days.